What's the Angle?

The two STEREO spacecraft have been slowly separating over most of the mission, so that now they are 44 degrees apart as of Jan. 8, 2008. They will continue to separate as the mission proceeds. So, what does this gain us? Well, for a time we could generate real 3D images and movies of the Sun for the first time. But there is another major advantage to the widening angle. At any given time, we get to see more and more of the Sun. Remember, until STEREO came along we could only watch the Sun each day from pretty much the Sun-Earth line of sight (as with SOHO).

Now, the Ahead spacecraft sees 22 degrees more around the right side--the Behind spacecraft sees 22 degrees more of the Sun to the left. Thus, we see 44 degrees more of the Sun's surface than we could before and that number will grow about 44 degrees each year. If all goes well, at some point we should be able to see the entire Sun from two opposing vantage points. The added bonus is that scientist can observe from a whole new perspective the progress, development and structure of solar storms from these two vantage points. The Behind view also helps us predict space weather by giving us a heads up on active regions which will soon be coming around to face Earth.